The present invention relates to an improved process for reducing a permanganate bleaching agent following its use in the bleaching of fabric which substantially reduces or eliminates the odor of sulfur dioxide, even when the reduction is carried out at elevated temperatures.
Garments having a faded or stone-washed appearance, particularly those made of blue denim, currently enjoy a considerable market, and several methods are known for chemically fading the fabric. For example, U.S. Pat. No. 4,218,220 and UK patent application No. 2 136 029 A both describe methods which avoid the actual use of stones in preparing faded fabrics. Nevertheless, commercial processes continue to utilize pumice stones in the preparation of faded fabrics.
In one such process, wet garments or fabric are tumbled in a commercial-type washing machine with abradable pumice stones which have been saturated with 3% potassium permanganate. The garments emerge from the "stone-wash" part of the process stained a rust brown color by the permanganate. This staining is removed in a subsequent washing step during which the permanganate is reduced to colorless water soluble materials.
In the known process, the permanganate is reduced with sodium metabisulfite, although other components such as optical brightners may also be added during the washing step. The use of sodium metabisulfite, however, results in a strong odor of sulfur dioxide (SO.sub.2) if high wash temperatures are employed. Thus, wash temperatures of 60.degree.-70.degree. F. are used, even though this increases the wash time required.
It is the object of the present invention to provide an improved reducing composition for use in permanganate-based fabric bleaching which permits the use of higher wash temperatures while substantially reducing or eliminating the odor of SO.sub.2.